The Deformed State and Nucleation of Recrystallization

Abstract

The phenomenon of nucleation of new grains during annealing of deformed metals is discussed with respect to various aspects of the deformed state, including the stored energy of cold work and various microstructural features. Attention is drawn to those regions of the deformed metal where there is a rapid change of orientation, such as pre-existing grain boundaries and deformation (transition) bands. The currently accepted theory of nucleation, the growth of favoured sub grains, is discussed in the light of the known low mobility of low-angle sub-boundaries. It is suggested that the high boundary mobility associated with misorentations > 10–18° is the origin of pre-existing grain boundaries and transition bands acting as principal sites for nucleation. Recent evidence concerning the initial growth of subgrain ‘nuclei’ is described and it is suggested that subgrain coalescence may often play a crucial role in this process. Subgrain coalscence appears to occur preferentially in those regions of lattice misorientation where, if such a ‘nucleus’ is formed, it can grow rapidly.